Crystalline form of a cephalosporin antibiotic

ABSTRACT

The preparation of a novel crystalline cefaclor and the conversion of such a product to cefaclor monohydrate are described. The new intermediate cefaclor is a particular crystalline form and possesses the same antibiotic properties as cefaclor monohydrate.

This is a continuation application of Ser. No. 08/235,262 (filed Apr.29, 1994--now abandoned), which is a continuation application of Ser.No. 07/973,457 (filed Nov. 9, 1992--now abandoned).

The present invention concerns a novel crystalline form of cefaclor, aprocess for its preparation and for its conversion to cefaclormonohydrate, as well as pharmaceutical compositions containing it asactive ingredient.

"Cefaclor" is the International Non-proprietary Name for7β-(D-2-amino-2-phenylacetamido)-3-chloro-3-cephem-4-carboxylic acid,represented by the formula (A), ##STR1## which is an orally activecefalosporin antibiotic.

Cefaclor for pharmaceutical use is a monohydrate, namely a compound offormula (A) with a molecule of water of crystallization.

The preparation of cefaclor monohydrate, which is not described in theliterature, involves a lot of difficulties due to the crystalline formitself of the antibiotic and to the methods for the synthesis of such anactive principle, which involve the use of polar aprotic solvents. U.S.Pat. No. 3,925,372 discloses the preparation of cefaclor by reaction ofthe methyl sodium Dane salt of D-phenylglycine with7-amino-3-chloro-3-cephem-4-carboxylic acid as silyl derivative and theisolation of cefaclor as hemihydrate.

The preparation of cefaclor is also described by R. R. Chauvette and P.A. Pennington in J. Med. Chem. 1975, 18, 403-408. By reacting the methylsodium Dane salt of D-phenylglycine with p-nitrobenzyl7-amino-3-chloro-3-cephem-4-carboxylate and by hydrogenating the productthus obtained in the presence of palladium on charcoal, cefaclor isobtained which crystallizes as hemihydrate.

It has now been found that, starting from a raw cefaclor, a novelcrystalline form of cefaclor is obtained, containing a water percentlower than that of the monohydrate and higher than that of thehemihydrate.

It has also surprisingly found that this new crystalline form ofcefaclor is stable in whatever moisture conditions and allows its use inpharmaceutical formulations which have the advantage, in respect ofthose comprising the monohydrate, of containing a higher amount ofactive ingredient per weight unit. By contrast, the hemihydrate form isdifficult to obtain in a reproducible way because of its instability.Finally, it has been found that the novel crystalline cefaclor, whichcannot be reconstituted by simple treatment with water in the warm, canbe converted to cefaclor monohydrate.

For this purpose, it must be dissolved in acidic medium and precipitatedin crystalline form at a suitable pH to isolate said monohydrate.

Thus, it is an object of present invention to provide a novelcrystalline form of cefaclor containing from 2.5% to 4.3% of water,advantageously from 2.6% to 4.2%. Preferably, the crystalline cefaclorof the invention contains 3.5% of water.

The crystalline cefaclor of the present invention exhibits the X-raysdiffraction pattern set forth in Table I. Such pattern, different fromthat of cefaclor monohydrate, has been detected, with the product of thepresent invention, as a powder, by using a PW diffractometer in theusual diffraction conditions (copper Kα radiations; curve graphitecrystal monochromator). The interplanar spacings are denoted as "d(A)"and the relative intensities are in the column "I%".

                  TABLE I                                                         ______________________________________                                                d(Å)                                                                            I %                                                             ______________________________________                                                11,55 67                                                                      9,56   8                                                                      8,45  17                                                                      7,93  29                                                                      6,72   8                                                                      5,94  15                                                                      5,78  22                                                                      5,59  28                                                                      5,38  11                                                                      5,19  97                                                                      4,83  56                                                                      4,62   3                                                                      4,51   8                                                                      4,44  11                                                                      4,27  100                                                                     4,06  15                                                                      3,97  83                                                                      3,87   9                                                                      3,79   7                                                                      3,68   2                                                                      3,59  28                                                                      3,53  13                                                                      3,47  38                                                                      3,34  15                                                                      3,25  18                                                                      3,18  31                                                                      3,08  33                                                                      2,94  12                                                                      2,89   7                                                                      2,81  10                                                                      2,74   7                                                              ______________________________________                                    

It is another object of the present invention to provide a process forthe preparation of the new crystalline cefaclor, characterized in thatcefaclor is treated with a mineral or organic acid in a from about 4/1(v/v) to about 1/4 (v/v) mixture of water and a substantiallywater-miscible alcohol until a complete solution is obtained, then thepH of the solution is adjusted to about 4.5, the temperature is broughtto 0°-5° C. and the product thus obtained is isolated.

The cefaclor used as starting material may be a raw cefaclor obtainedaccording to one of the methods described in the literature, for exampleaccording to U.S. Pat. No. 3,925,372 or to J. Med. Chem. 1975, 18,403-408 (to which reference is made herein for further details), byexcluding the final operation of recovery of the product as hemihydrate.

A raw cefaclor particularly suitable as starting material is anamorphous cefaclor obtained by reacting a D-phenylglycine Dane salt,preferably the ethyl 3-α-carboxybenzylaminocrotonate potassium salt(obtained from D-phenylglycine and ethyl acetoacetate), with thetriethylamine salt of 7-amino-3-chloro-3-cephem-4-carboxylic acid in anacetonitrile/dimethylformamide/water mixture and isolating the productby acidification of the mixture and correction of pH to a value of 4.5.Crystalline cefaclor with different hydratation degree may also be usedas starting materials.

The alcohol-water mixture used for the preparation of crystallinecefaclor consists in preferably deionized water and in a water-misciblealcohol, preferably an aliphatic alcohol containing from 1 to 4 carbonatoms, from example methanol, ethanol, isopropanol.

The amount of the mineral or organic acid used is that which allows thesolution of the raw cefaclor. Suitable acids, for example, arehydrochloric, hydrobromic, sulfuric, phosphoric, methanesulfonic,trifluoroacetic acids. Preferably an aqueous solution of hydrochloricacid is used. Crystalline cefaclor is isolated at a pH of about 4.5 bysimple cooling and filtration.

The pH of about 4.5 is reached by treating the acid solution with aninorganic or organic base such as an alkaline hydroxide, for examplesodium hydroxide, ammonium hydroxide, or an amine, for exampletrimethylamine, triethylamine, N-methylpiperidine, N-methylmorpholine,triethylamine and ammonium hydroxide being the preferred bases.

The product thus obtained is stable and may be used as such for thepreparation of oral pharmaceutical compositions, for example in gelatinecapsules, tablets, granulates, alone or in admixture with the usualpharmaceutical carriers. Such pharmaceutical compositions comprisecrystalline cefaclor according to the present invention in amountsequivalent to 125-750 mg, preferably 250 or 500 mg, of anhydrouscefaclor.

Alternatively, crystalline cefaclor thus obtained may be used for thepreparation of cefaclor monohydrate. Such an use is provided by afurther object of the present invention. Such an use involves a processfor the conversion of crystalline cefaclor into cefaclor monohydratewhich comprises acidifying an aqueous suspension of the above describedcrystalline cefaclor until a complete solution is obtained, adjustingthe pH to about 4.5 and isolating the product thus obtained.

Preferably the process is carried out by acidifying an aqueoussuspension of crystalline cefaclor until a complete solution isobtained, then by increasing the pH of the solution to 1.5.

The monohydrate begins to precipitate or a crystal of authentic cefaclormonohydrate is added to initiate the precipitation. By adjusting the pHof the solution to about 4.5 at room temperature (20° to 30° C.) slowlyand cooling, the precipitation is completed and cefaclor monohydrate isrecovered by filtration.

Preferably, crystalline cefaclor is dissolved by using a mineral ororganic acid such as hydrochloric, hydrobromic, sulphuric, phosphoric,methanesulfonic or trifluoroacetic acid and the increase of pH to about4.5 is obtained by using a inorganic or organic base like those abovementioned, for example ammonium hydroxide, sodium hydroxide, trimethylamine or triethylamine, triethylamine and ammonium hydroxide beingpreferred.

Thus cefaclor, preferably in amorphous form, may be converted tocefaclor monohydrate by a two-steps process, which comprises

(i) treating cefaclor with a mineral or organic acid in a from about 4/1(v/v) to about 1/4 (v/v) mixture of water and a substantiallywater-miscible alcohol until a complete solution is obtained, adjustingthe pH of the solution to about 4.5, bringing the temperature of thesolution to 0°÷5° C. and isolating the crystalline cefaclor thusobtained; then

(ii) acidifying an aqueous suspension of said crystalline cefaclor untila complete solution is obtained, adjusting the pH to about 4.5 andisolating the cefaclor monohydrate thus obtained.

The following examples illustrate the invention without, however,limiting it.

EXAMPLE 1

Amorphous raw cefaclor

To a mixture of 162 g of ethyl 3-α-carboxybenzylaminocrotonate potassiumsalt, 450 ml of dimethylformamide and 900 ml of acetonitrile, cooled to-40° C., 1.5 ml of 4-methylmorpholine and 54 ml of ethyl chloroformateare added. The mixture is stirred one hour at -40° C., then a previouslycooled solution of triethylamine salt of7-amino-3-chloro-3-cephem-4-carboxylic acid (corresponding to 99 g offree acid) in 900 ml of a mixture acetonitrile/water 1/1 (v/v) is addedthereinto. The solution is kept in the cool for about 3 hours, then itis treated with 630 ml of water and filtered. The filtrate is made acidto pH 1.5 with 6N hydrochloric acid, then the pH is adjusted to 4.5 withtriethyl amine. The suspension thus obtained is kept to 0° C. overnight,then it is filtered. The product thus obtained is washed withacetonitrile/ water 1/1 (v/v) and dried under vacuum at 35° C.

Thus, 120 g of amorphous raw cefaclor are obtained.

EXAMPLE 2

(a) Condensation

To a mixture of 300 ml of acetonitrile and 180 ml of dimethyl formamide,at 0° C., 54 g of ethyl 3-α-carboxybenzylaminocrotonate potassium saltare added. The mixture is cooled to -40° C. and 18 ml of ethylchloroformate and 0.25 ml of 4-methylmorpholine are added thereinto. Themixture is kept one hour at -40° C., then it is treated with apreviously to 0° C. cooled solution of silylated7-amino-3-chloro-3-cephem-4-carboxylic acid (obtained from 33 g of freeacid with bis-trimethylsilylacetamide) in 300 ml of aceto nitrile. Thesolution is kept 2 hours at -40° C., then it is diluted with 210 ml ofwater, acidified with 6N hydrochloric acid to pH 1.5 and filtered toeliminate the undissolved products. The pH of the clear solution isadjusted to 4.5 with triethylamine and the suspension is filtered.

(b) Crystallization

The wet product thus obtained is dissolved in a with diluted hydrochloric acid acidified mixture of 250 ml of water and 250 ml ofmethanol. The mixture is decolorized with charcoal, filtered, cooled to+5° C. and brought to pH 4.5 with triethylamine.

Then it is filtered, the product is washed with water and dried "invacuo" at 35° C.

Thus, 30.4 g of crystalline cefaclor containing 2.8% of water areobtained.

EXAMPLE 3

(a) Condensation

To a previously to -40° C. cooled mixture of 300 ml of acetonitrile, 180ml of dimethylformamide and 54 g of ethyl 3-α-carboxybenzylaminocrotonate potassium salt, 18 ml of ethyl chloroformate and 0.25 mlof 4-methylmorpholine are added. After one hour at -40° C. a solution at0° C. of the 7-amino-3-chloro-3-cephem-4-carboxylic acid triethylaminesalt (obtained from 33 g of free acid and triethyl amine) in 300 ml ofacetonitrile/water 1/1 (v/v) is added thereinto. The solution is kept 3hours at -40° C. under stirring, then water is added thereinto and theundissolved part is eliminated by filtration. The clear solution is madeacid with 6N hydrochloric acid until pH 1.5, then the pH is adjusted to4.5 with triethyl amine and the product obtained is filtered and washedwith acetonitrile/water 2/1 (v/v).

(b) Crystallization

To a suspension of the wet product thus obtained in 500 ml of a mixturemethanol/water 1/1 (v/v), 6N hydrochloric acid is added until a clearsolution is obtained. The solution is decolorized with charcoal andfiltered. Its pH is adjusted to a final value of 4.5 by slow addition oftriethylamine. The solution is cooled to 0° C. and kept at thistemperature for 2 hours, then it is filtered, washed with cool water anddried at 40° C. "in vacuo". Thus, 32 g of crystalline cefaclorcontaining 3.5% of water and having a HPLC purity of 98% are obtained.The thermogravimetric analysis (TGA) of the product shows, from 22° to120° C., a weight loss of about 3.5% which exactly corresponds to thecrystallization water, as appears in FIG. 1. FIG. 2 shows the IRspectrum of the product in KBr.

EXAMPLE 4

Crystallization

To a suspension of 11 g of amorphous raw cefaclor, obtained as describedin Example 1, in 66 ml of a mixture methanol/water 2/1 (v/v), 6Nhydrochloric acid is added until a clear solution is obtained. Thissolution is decolorized with charcoal, its pH is adjusted withtriethylamine to reach a value of 4.5 in 2 hours, then it is cooled to0° C., kept at this temperature for 2 hours and finally filtered. Therecovered product is washed with a mixture methanol/water 2/1 (v/v) anddried under vacuum.

Thus, 8.2 g of crystalline cefaclor containing 2.8% of water areobtained.

EXAMPLE 5

Crystallization

To a suspension of 20 g of raw cefaclor, obtained as described inExample 1, in 90 ml of a solution methanol/water 2/1 (v/v), 6Nhydrochloric acid is added until a complete solution is obtained. Thissolution is decolorized, filtered and treated, in about 90 minutes at 0°C., with 50 ml of water, by keeping the pH constant at 4.5 by concurrentaddition of triethylamine. The suspension is kept one hour at 0° C.,then it is filtered and the recovered product is dried under vacuum.

Thus, 14.8 g of crystalline cefaclor containing 3.2% of water areobtained.

EXAMPLE 6

Crystallization

To a suspension of 36 g of amorphous raw cefaclor, obtained as describedin Example 1, in 300 ml of a solution ethanol/water 1/1 (v/v), 6Nhydrochloric acid is added until a complete solution. This solution isdecolorized with charcoal, filtered and its pH is adjusted by additionof triethylamine to reach the value of 4.5 in about 2 hours.

Then it is cooled to 0° /+5° C., kept at this temperature for additional2 hours and filtered. The product recovered is washed with water anddried under vacuum.

Thus, 28.5 g of crystalline cefaclor containing 3.7% of water areobtained.

EXAMPLE 7

Crystallization

To a suspension of 10 g of amorphous raw cefaclor, obtained as describedin Example 1, in 60 ml of isopropanol/water 1/4 (v/v) 6N hydrochloricacid is added until the obtention of a solution which is decolorizedwith charcoal and filtered. The pH of the solution is adjusted to reachthe value of 4.5 in 180 minutes by addition of triethylamine. Thesolution is cooled to 0° C., kept at this temperature overnight, thenfiltered. The recovered product is washed with water and dried undervacuum at 40° C.

Thus, 7.8 g of crystalline cefaclor containing 4.1% of water areobtained.

EXAMPLE 8

Crystallization

To a mixture of 550 ml of methanol and 550 ml of deionized water 114 gof amorphous raw cefaclor, obtained as described in Example 1, aresuspended. To the suspension 70 ml of 6N hydrochloric acid are added in30 minutes under stirring, whereby a complete solution is obtained (pHof about 1.5). After decolorizing with charcoal, triethylamine is slowlyadded to the clear solution to a pH value of 2.1. The solution isstirred until crystallization begins, then triethylamine is added againuntil a pH of 4.5 is obtained and the crystallization is thus complete.The mixture is cooled to 0° C. and kept 2 hours at this temperature,then it is filtered. The recovered product is washed with deionized coolwater and dried under vacuum.

Thus, 84 g of crystalline cefaclor containing 3.5% water are obtained.In the following examples some illustrative pharmaceutical formulationsfor oral use containing crystalline cefaclor are given.

EXAMPLE 9

Tablets containing:

crystalline cefaclor (containing 3,5% water) 259 mg

equivalent to 250 mg of anhydrous cefaclor sodium laurylsulfate 5 mg

starch 10 mg

microcrystalline cellulose q.s. to 500 mg

EXAMPLE 10

Hard Gelatine Capsules containing:

crystalline cefaclor (containing 3,5% water) 518 mg

equivalent to 500 mg of anhydrous cefaclor starch 6-12 mg

finely subdivided silica 3-6 mg

EXAMPLE 11

Granulate for reconstituted suspension (250 mg/5 ml) containing:

crystalline cefaclor (containing 3,5% water) 259 mg

equivalent to 250 mg of anhydrous cefaclor low viscosity sodiumcarboxymethylcellulose 90 mg

orange flavour 5 mg

starch 15 mg

sucrose 1800 mg

EXAMPLE 12

Preparation of cefaclor monohydrate

To a suspension of 82 g of crystalline cefaclor, obtained as describedin Example 7, in 500 ml of deionized water 50 ml of 6N hydrochloric acidare added under stirring at about 15° C. until a complete solution isobtained. The solution thus obtained, having a pH of about 0.7, isdecolorized, then ammonium hydroxide is added to the clear solution atpH 1.5. The crystallization is initiated by crystalline cefaclormonohydrate as seed, then ammonium hydroxide is added again in 4 hoursup to a constant pH of 4.5. The mixture is kept under stirring for 30minutes at 25° C., then it is cooled at about 0° C. and kept 2 hours at0° ÷5° C. The recovered product is filtered, washed with cool deionizedwater and dried under vacuum at 35° C.

Thus, 67-68 g of crystalline cefaclor monohydrate are obtained. It's IRand X-rays analysis is in agreement with the official standard.

We claim:
 1. A crystalline cefaclor having a water content of from 2.5%to 4.3% and showing the following powder X-rays diffraction pattern:

    ______________________________________                                        d(A)                  I %                                                     ______________________________________                                        11,55                 67                                                      9,56                  8                                                       8,45                  17                                                      7,93                  29                                                      6,72                  8                                                       5,94                  15                                                      5,78                  22                                                      5,59                  28                                                      5,38                  11                                                      5,19                  97                                                      4,83                  56                                                      4,62                  3                                                       4,51                  8                                                       4,44                  11                                                      4,27                  100                                                     4,06                  15                                                      3,97                  83                                                      3,87                  9                                                       3,79                  7                                                       3,68                  2                                                       3,59                  28                                                      3,53                  13                                                      3,47                  38                                                      3,34                  15                                                      3,25                  18                                                      3,18                  31                                                      3,08                  33                                                      2,94                  12                                                      2,89                  7                                                       2,81                  10                                                      2,74                 
 7.                                                      ______________________________________                                    


2. A crystalline cefaclor according to claim 1, having a water contentof 3.5%.
 3. A process for the preparation of crystalline cefaclor ofclaim 1 which comprises treating cefaclor with a mineral or organic acidin a from about 4/1 (v/v) to about 1/4 (v/v) mixture of water and asubstantially water-miscible alcohol until a complete solution isobtained, then adjusting the pH of the solution to about 4.5, bringingthe temperature of the solution to 0°-5° C. and isolating the productthus obtained.
 4. A process according to claim 3 in which thesubstantially water-miscible alcohol is an aliphatic alcohol containingfrom 1 to 4 carbon atoms.
 5. A process according to claim 4 wherein thealcohol is selected from the group consisting of methanol, ethanol andisopropanol.
 6. A process according to claim 3 wherein hydrochloric acidis used as a mineral acid.
 7. A process according to claim 3 in whichammonium hydroxide or triethylamine is used to adjust the pH to about4.5.
 8. A process according to claim 3 which comprises furtheracidifying an aqueous suspension of the crystalline cefaclor thusisolated until a complete solution is obtained, adjusting the pH toabout 4.5 and isolating the cefaclor monohydrate thus obtained.
 9. Aprocess as claimed in claim 8 in which the aqueous suspension is madeacid by hydrochloric acid.
 10. A process according to claim 9 in whichthe increase of the pH to about 4.5 is obtained by using triethylamineor ammonium hydroxide.
 11. A pharmaceutical composition for oral usecomprising an amount of crystalline cefaclor according to claim 1corresponding to 125 to 750 mg of anhydrous cefaclor in admixture with apharmaceutical carrier.
 12. A pharmaceutical composition for oral usecomprising an amount of crystalline cefaclor according to claim 2corresponding to 125 to 750 mg of anhydrous cefaclor in admixture with apharmaceutical carrier.